Adaptation of Conduit Artery Vascular Smooth Muscle Tone to Induced Hypertension

We studied the changes in vascular smooth muscle (VSM) cell tone during the adaptation of rat common carotids to induced hypertension. Hypertension was induced in 8 week old male Wistar rats by total ligation of the aorta between the two kidneys. Mean blood pressure increased abruptly from 92±2 mm Hg (mean±SE) to 145±4 mm Hg and remained constant thereafter. Rats were sacrificed 2, 4, 8, and 56 days after surgery and the left common carotid artery was excised for analysis. Pressure-diameter curves were measured in vitro under normal, maximally contracted, and totally relaxed VSM. The VSM tone was analyzed in terms of its basal tone (active stress at low strains) and its myogenic tone (increase in active stress at high strains). Our results show that the capacity of the VSM to develop maximal active stress is not altered in hypertension. Basal tone, however, increases rapidly in the acute hypertension phase (2-8 days postsurgery) and drops to nearly control values at 56 days postsurgery. Also, the onset of myogenic response decreases to lower strains following the step change in pressure, to be restored back to control levels at 56 days postsurgery. We conclude that VSM adaptation is most significant in the acute hypertension phase and acts as a first, rapid defense mechanism for the arterial wall. The VSM tone returns back to normal levels once the slower geometrical and structural remodeling is developed sufficiently to restore the biomechanical environment and function of the arterial wall to control levels. © 2002 Biomedical Engineering Society. PAC2002: 8719Rr, 8719Ff, 8719U

The non-circular shape of FloWatch®-PAB prevents the need for pulmonary artery reconstruction after banding: Computational fluid dynamics and clinical correlations

Objective: To evaluate the differences between non-circular shape of FloWatch®-PAB and conventional pulmonary artery (PA) banding. Methods: Geometrical analysis. Conventional banding and FloWatch®-PAB perimeters were plotted against cross-sections. Computational fluid dynamics (CFD) model. CFD compared non-circular FloWatch®-PAB cross-sections with conventional banding regarding pressure gradients. Clinical data. Seven children, median age 2 months (7 days to 3 years), median weight 4.2 kg (3.2-9.8 kg), with complex congenital heart defects underwent PA banding with FloWatch®-PAB implantation. Results: Geometrical analysis. Conventional banding: progressive reduction of cross-sections was accompanied by progressive reduction of PA perimeters. FloWatch®-PAB: with equal reduction of cross-sections the PA perimeter remained constant. CFD model. Non-circular and circular banding provided same trans-banding pressure gradients for same cross-sections at any given flow. Clinical data. Mean PA internal diameter at banding was 13.3 ± 4.5 mm. After a mean interval of 5.9 ± 3.7 months, all children underwent intra-cardiac repair and simple FloWatch®-PAB removal without PA reconstruction. Mean PA internal diameter with FloWatch®-PAB removal increased from 3.0 ± 0.8 to 12.4 ± 4.5 mm (normal mean internal diameter for the age = 9.9 ± 1.6). No residual pressure gradient was recorded in correspondence of the site of the previous FloWatch®-PAB implantation in 6/7 patients, 10 mmHg peak and 5 mmHg mean gradient in 1/7. Conclusions: The non-circular shape of FloWatch®-PAB can replace conventional circular banding with the following advantages: (a) the pressure gradient will remain essentially the same as for conventional circular banding for any given cross-section, but with significantly smaller reduction of PA perimeter; and (b) PA reconstruction at the time of de-banding for intra-cardiac repair can be avoide

The non-circular shape of FloWatch®-PAB prevents the need for pulmonary artery reconstruction after banding

To evaluate the differences between non-circular shape of FloWatch®-PAB and conventional pulmonary artery (PA) banding. Methods: Geometrical analysis. Conventional banding and FloWatch®-PAB perimeters were plotted against cross-sections. Computational fluid dynamics (CFD) model. CFD compared non-circular FloWatch®-PAB cross-sections with conventional banding regarding pressure gradients. Clinical data. Seven children, median age 2 months (7 days to 3 years), median weight 4.2 kg (3.2–9.8 kg), with complex congenital heart defects underwent PA banding with FloWatch®-PAB implantation. Results: Geometrical analysis. Conventional banding: progressive reduction of cross-sections was accompanied by progressive reduction of PA perimeters. FloWatch®-PAB: with equal reduction of cross-sections the PA perimeter remained constant. CFD model. Non-circular and circular banding provided same trans-banding pressure gradients for same cross-sections at any given flow. Clinical data. Mean PA internal diameter at banding was 13.3 ± 4.5 mm. After a mean interval of 5.9 ± 3.7 months, all children underwent intra-cardiac repair and simple FloWatch®-PAB removal without PA reconstruction. Mean PA internal diameter with FloWatch®-PAB removal increased from 3.0 ± 0.8 to 12.4 ± 4.5 mm (normal mean internal diameter for the age = 9.9 ± 1.6). No residual pressure gradient was recorded in correspondence of the site of the previous FloWatch®-PAB implantation in 6/7 patients, 10 mmHg peak and 5 mmHg mean gradient in 1/7. Conclusions: The non-circular shape of FloWatch®-PAB can replace conventional circular banding with the following advantages: (a) the pressure gradient will remain essentially the same as for conventional circular banding for any given cross-section, but with significantly smaller reduction of PA perimeter; and (b) PA reconstruction at the time of de-banding for intra-cardiac repair can be avoided

Adaptation of conduit artery vascular smooth muscle tone to induced hypertension

We studied the changes in vascular smooth muscle (VSM) cell tone during the adaptation of rat common carotids to induced hypertension. Hypertension was induced in 8 week old male Wistar rats by total ligation of the aorta between the two kidneys. Mean blood pressure increased abruptly from 92 +/- 2mm Hg (mean +/- SE) to 145 +/- 4 mm Hg and remained constant thereafter. Rats were sacrificed 2, 4, 8, and 56 days after surgery and the left common carotid artery was excised for analysis. Pressure-diameter curves were measured in vitro under normal, maximally contracted, and totally relaxed VSM. The VSM tone was analyzed in terms of its basal tone (active stress at low strains) and its myogenic tone (increase in active stress at high strains). Our results show that the capacity of the VSM to develop maximal active stress is not altered in hypertension. Basal tone, however, increases rapidly in the acute hypertension phase (2-8 days postsurgery) and drops to nearly control values at 56 days postsurgery. Also, the onset of myogenic response decreases to lower strains following the step change in pressure, to be restored back to control levels at 56 days postsurgery. We conclude that VSM adaptation is most significant in the acute hypertension phase and acts as a first, rapid defense mechanism for the arterial wall. The VSM tone returns back to normal levels once the slower geometrical and structural remodeling is developed sufficiently to restore the biomechanical environment and function of the arterial wall to control levels

The non-circular shape of FloWatch-PAB prevents the need for pulmonary artery reconstruction after banding. Computational fluid dynamics and clinical correlations

OBJECTIVE: To evaluate the differences between non-circular shape of FloWatch-PAB and conventional pulmonary artery (PA) banding. METHODS: Geometrical analysis. Conventional banding and FloWatch-PAB perimeters were plotted against cross-sections. Computational fluid dynamics (CFD) model. CFD compared non-circular FloWatch-PAB cross-sections with conventional banding regarding pressure gradients. Clinical data. Seven children, median age 2 months (7 days to 3 years), median weight 4.2 kg (3.2-9.8 kg), with complex congenital heart defects underwent PA banding with FloWatch-PAB implantation. RESULTS: Geometrical analysis. Conventional banding: progressive reduction of cross-sections was accompanied by progressive reduction of PA perimeters. FloWatch-PAB: with equal reduction of cross-sections the PA perimeter remained constant. CFD model. Non-circular and circular banding provided same trans-banding pressure gradients for same cross-sections at any given flow. Clinical data. Mean PA internal diameter at banding was 13.3+/-4.5 mm. After a mean interval of 5.9+/-3.7 months, all children underwent intra-cardiac repair and simple FloWatch-PAB removal without PA reconstruction. Mean PA internal diameter with FloWatch-PAB removal increased from 3.0+/-0.8 to 12.4+/-4.5 mm (normal mean internal diameter for the age=9.9+/-1.6). No residual pressure gradient was recorded in correspondence of the site of the previous FloWatch-PAB implantation in 6/7 patients, 10 mmHg peak and 5 mmHg mean gradient in 1/7. CONCLUSIONS: The non-circular shape of FloWatch-PAB can replace conventional circular banding with the following advantages: (a) the pressure gradient will remain essentially the same as for conventional circular banding for any given cross-section, but with significantly smaller reduction of PA perimeter; and (b) PA reconstruction at the time of de-banding for intra-cardiac repair can be avoided

Deformation and Grain Growth of Low-Temperature-Sintered High-Purity Alumina

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/66091/1/j.1151-2916.1990.tb06489.x.pd